Direct strength method for the design of purlins

Abstract

The Direct Strength Method (DSM) has recently been developed for the design of cold-formed steel structural members. What is now required is the calibration of the method against existing design methodologies for common structural systems such as roof and wall systems. The chapter firstly explains the application of the DSM for the design of simply supported and continuous purlins. Some generalizations, such as how to handle combined bending and shear at the ends of laps, have had to be made to implement the method for continuous purlin systems. The method is applied to study a range of section sizes in C- and Z-sections and a range of spans for simply supported, continuous and continuous lapped purlins. This standard is similar to the AISI Specification except that it includes design rules for distortional buckling. Some modifications have had to be made to the strength equations in the DSM to achieve an accurate and reliable comparison. These modifications are included in the chapter. The DSM is a newly proposed approach for determining the strength of cold-formed members. Conventionally, the effective width method has been used as recognized in the current cold-formed steel design standards. The DSM however uses full section properties with an appropriate strength design curve to give a direct strength. The purpose of this research is to compare the results of the DSM with the effective width method. To achieve this objective, a series of tables for purlin capacity is created using the DSM for comparison with those based on the effective width method.